#=======================================================================
#
#   Python Lexical Analyser
#
#   Lexical Analyser Specification
#
#=======================================================================

import types

from plex import actions
from plex import dfa as DFA
from plex import errors
from plex import machines
from plex import regexps

# debug_flags for Lexicon constructor
DUMP_NFA = 1
DUMP_DFA = 2


class State:
    """
    This class is used as part of a Plex.Lexicon specification to
    introduce a user-defined state.

    Constructor:

        State(name, token_specifications)
    """

    name = None
    tokens = None

    def __init__(self, name, tokens):
        self.name = name
        self.tokens = tokens


class Lexicon:
    """
    Lexicon(specification) builds a lexical analyser from the given
    |specification|. The specification consists of a list of
    specification items. Each specification item may be either:

        1) A token definition, which is a tuple:

                (pattern, action)

            The |pattern| is a regular axpression built using the
            constructors defined in the Plex module.

            The |action| is the action to be performed when this pattern
            is recognised (see below).

        2) A state definition:

                State(name, tokens)

            where |name| is a character string naming the state,
            and |tokens| is a list of token definitions as
            above. The meaning and usage of states is described
            below.

    Actions
    -------

    The |action| in a token specication may be one of three things:

        1) A function, which is called as follows:

            function(scanner, text)

        where |scanner| is the relevant Scanner instance, and |text|
        is the matched text. If the function returns anything
        other than None, that value is returned as the value of the
        token. If it returns None, scanning continues as if the IGNORE
        action were specified (see below).

        2) One of the following special actions:

            IGNORE means that the recognised characters will be treated as
                   white space and ignored. Scanning will continue until
                   the next non-ignored token is recognised before returning.

            TEXT   causes the scanned text itself to be returned as the
                   value of the token.

        3) Any other value, which is returned as the value of the token.

    States
    ------

    At any given time, the scanner is in one of a number of states.
    Associated with each state is a set of possible tokens. When scanning,
    only tokens associated with the current state are recognised.

    There is a default state, whose name is the empty string. Token
    definitions which are not inside any State definition belong to
    the default state.

    The initial state of the scanner is the default state. The state can
    be changed in one of two ways:

        1) Using Begin(state_name) as the action of a token.

        2) Calling the begin(state_name) method of the Scanner.

    To change back to the default state, use '' as the state name.
    """

    machine = None # Machine
    tables = None # StateTableMachine

    def __init__(self, specifications, debug=None,
                 debug_flags=7, timings=None):
        if type(specifications) <> types.ListType:
            raise errors.InvalidScanner("Scanner definition is not a list")

        if timings:
            from plex.timing import time
            total_time = 0.0
            time1 = time()

        nfa = machines.Machine()
        default_initial_state = nfa.new_initial_state('')
        token_number = 1
        for spec in specifications:
            if isinstance(spec, State):
                user_initial_state = nfa.new_initial_state(spec.name)
                for token in spec.tokens:
                    self.add_token_to_machine(
                        nfa, user_initial_state, token, token_number)
                    token_number = token_number + 1

            elif type(spec) == types.TupleType:
                self.add_token_to_machine(
                    nfa, default_initial_state, spec, token_number)
                token_number = token_number + 1
            else:
                raise errors.InvalidToken(
                    token_number,
                    "Expected a token definition (tuple) or State instance")

        if timings:
            time2 = time()
            total_time = total_time + (time2 - time1)
            time3 = time()

        if debug and (debug_flags & 1):
            debug.write("\n============= NFA ===========\n")
            nfa.dump(debug)

        dfa = DFA.nfa_to_dfa(nfa, debug=(debug_flags & 3) == 3 and debug)

        if timings:
            time4 = time()
            total_time = total_time + (time4 - time3)

        if debug and (debug_flags & 2):
            debug.write("\n============= DFA ===========\n")
            dfa.dump(debug)

        if timings:
            timings.write("Constructing NFA : %5.2f\n" % (time2 - time1))
            timings.write("Converting to DFA: %5.2f\n" % (time4 - time3))
            timings.write("TOTAL            : %5.2f\n" % total_time)

        self.machine = dfa

    def add_token_to_machine(self, machine, initial_state, token_spec,
                             token_number):
        try:
            (re, action_spec) = self.parse_token_definition(token_spec)
            # Disabled this -- matching empty strings can be useful
            #if re.nullable:
            #  raise errors.InvalidToken(
            #    token_number, "Pattern can match 0 input symbols")
            if isinstance(action_spec, actions.Action):
                action = action_spec

            elif callable(action_spec):
                action = actions.Call(action_spec)

            else:
                action = actions.Return(action_spec)
            final_state = machine.new_state()
            re.build_machine(machine, initial_state, final_state,
                             match_bol=1, nocase=0)
            final_state.set_action(action, priority=-token_number)
        except errors.PlexError, e:
            raise e.__class__("Token number %d: %s" % (token_number, e))

    def parse_token_definition(self, token_spec):
        if type(token_spec) <> types.TupleType:
            raise errors.InvalidToken("Token definition is not a tuple")

        if len(token_spec) <> 2:
            raise errors.InvalidToken(
                "Wrong number of items in token definition")

        pattern, action = token_spec

        if not isinstance(pattern, regexps.RE):
            raise errors.InvalidToken("Pattern is not an RE instance")

        return (pattern, action)

    def get_initial_state(self, name):
        return self.machine.get_initial_state(name)
